Hydro-cyclones



United States Patent 3,139,157 HYDRG-CYCLONES Denis F. Kelsall, 154Beach Road, Sandringham, Melbourne, Victoria, Australia, and Jack A.Holmes, Plot 1202 Lincoln Ave., Kitwe, Northern Rhodesia Filed Dec. 15,1959, Ser. No. 43,269 Claims priority, application Republic of SouthAfrica Dec. 15, B58 (Filed under Rule 476)) and 35 U..C. 118) 1 Claim.(Cl. 210-512) This invention relates to hydro-cyclones such as are usedfor the classification of metallurgical pulps.

In a hydro-cyclone pulp is introduced tengentially at the feed end of acontainer. Axially at the same end there is a vortex finder throughwhich fine particles, and a proportion of the conveying liquid aredischarged. At the point axially opposed to the vortex finder there is adischarge of dense pulp. The object is that the coarse particles shouldfind their way into the dense pulp, and that the fine particles shouldbe discharged through the vortex finger. The container may have a widevariety of shapes, all of which are well-known in the art.

With known hydro-cyclones it has been found that the coarse orfaster-settling particles in the underflow carry fine particles in thevoids among them. The presence of such fine, or slower settlingparticles in the underfiow is undesirable as it lowers the overallefficiency of the classification. There have been proposals forincreasing the ethciency of classification by adding hydraulic liquidnear the underfiow aperture to wash entrained slirnes from it. Theseproposals have not been proved to be very practicable.

An object of the invention is to improve efiiciency of classification bydecreasing the proportion of fine particles in the underfiow pulp of ahydro-cyclone.

According to the invention the underfiow is discharged into a cyclonicchamber where clear liquid is introduced tangentially in the samedirection as in the main cyclone, and pulp withdrawn axially in thenormal way. In other words, the pulp from the main hydro-cyclone isdischarged through the vortex finder of this cyclonic chamber. Inpractice it is found that the cyclonic action in the second chamberWashes fine particles from between the voids of the pulp entering it, orthat a barrier is set up in the chamber through which fine particlescannot pass. As a result of the relatively low volume of clear liquidrequired to wash out fine particles the pulp densities of both cycloneproducts may not be significantly afected.

In the preferred form of the invention the main cyclone and cyclonicchamber have a party wall which may be a surface which, in the directionof the discharge, is concave or convex to the interior of the cyclone,and the peripheral diameter of which coincides with the internaldiameter of the main cyclone at a certain position or positions. Thisparty wall has been termed the cone piece and is usually a truncatedright circular conical shell. The discharge from the main cyclone isthus an aperture in the cone piece and this aperture also constitutesthe vortex finder of the cyclonic chamber.

It should be noted (as said above) that the direction of entry of theclear liquid into the cyclonic chamber is such that liquid in thatchamber conforms in its direction of swirl with the direction of swirlimposed by the feed of the main cyclone.

The invention is further discussed with reference to the accompanyingdrawings, in which:

FIGURE 1 is a section through a hydrocyclone according to the invention,

FIGURE 2 is a diagrammatic view of a further type of hydro-cyclone,

3,130,157 Patented Apr. 21, 1964 FIGURE 3 is a diagrammatic view ofanother type, and

FIGURE 4 is a diagrammatic view of a fourth type.

The cyclone illustrated in FIGURE 1 firstly has the conventionalcyclonic chamber 5 defined by an end wall 6, a cylindrical shell 7, anda truncated conical shell 8. The side walls of the frustoconical portion8 slope downwardly in such a manner that the apparent apex of thisfrustoconical portion has an acute inclined angle in vertical sectionsubstantially less than In the normal Way the cylindrical shell 7 isprovided with one or more feed ducts 9. A vortex finder l9 pierces theend wall 6 in the normal way.

As against standard practice the conical shell 7 terminates at arelatively wide diameter where it intersects a symmetrically taperedright circular shell or cone piece 11 with an aperture 12 thatconstitutes the underfiow aperture of. the chamber 5. The cone piece orfrustoconical party wall 11 tapers in the direction of the underilow insuch a manner that the apparent apex has an obtuse included angle invertical section substantially greater than 90 To the other side of thecone piece 11 there is a further cyclonic chamber 13, that has acylindrical shell 14, and a terminal portion 15 constituted by atruncated conical shell. The opening 16 in the portion 15 constitutesthe discharge from the apparatus. The shell 14 is provided with a seriesof inlet ducts 17. The direction of the ducts 17 is such that liquidforced in under pressure through them causes a swirling flow in thechamber 13 which has the same rotational sense as the swirling flowcaused by liquid entering the ducts 9 into the chamber 5.

In use pulp enters the ducts 9 in the normal way. The slimes fractionleaves the chamber 5 via the vortex finder l0 and the thickened pulphaving fines entrained among the voids therein leaves the chamberthrough the discharge aperture 12. Before leaving the chamber, however,the pulp which is descending along the sloping walls of the conicalshell 8 abruptly changes its direction of movement so that it travelsinwardly toward the axis of the chamber. The pulp now descending at amaterially slower rate due to the abrupt change in the direction of itstravel enters the chamber 13 where it encounters a cyclone of clearliquid fed in through the ducts 17. In passing through the chamber 13the thickened pulp gets denuded of line particles contained between thevoids or" coarse particles and the percentage of fine particlesreporting in the discharge from the opening 16 is significantlydecreased.

The most important operating features are as follows:

(1) The underfiow aperture 16 of the cyclone must be large enough toaccommodate the feed rate to the cyclone of solid particles whoseseparation into the underfiow is desired and should be situated asuitable distance from clear liquid inlet 17 such that as thick anunderfiow as is desired is in fact obtained.

(2) The rate of injection of clear liquid into the cyclonic chamber 13must be sufiicient to displace the desired proportion of entrainedslimes from between the voids of the faster settling particles.

(3) The cone piece aperture 16 must be large enough to accommodate thefeed rate to the cyclone of solid particles Whose separation to theunderfiow is required, having regard to the back pressure which isexerted by clear liquid injected into the cyclonic chamber 13 andpassing back into the main cyclone chamber 5.

(4) The feed rate must not be such as to overload the cyclone, that is,the cyclone should not be fed solid particles to be classified at such arate that the efficiency of classification is poor and the quality ofthe overflow or underfiow product, or of both products, is seriouslyimpaired.

3 (5) The feed and overflow apertures are not affected and are adjustedaccording to conventional practice.

In a rest run figures in the following table were obtained:

Flow rate of injected water, l./min -I 3. 5 Percentage of total wateradded reporting in the underflow stream 33. 27.8 Percentage of the minus10p particles in the feed reporting in the underflow stream 43. 0 11.Injection water flow rate as a percentage of water flow rate to theundcrfiow stream. 68. 1 Pulp density of the underflow stream,

percent w./w. solids 58. 7 49. 9

Pulp density of the overflow stream, percent w./w. solids 4. 2 4. 2

Percentage of particles larger than 25 microns in the solids whichreport in the overflow stream 3. 6 2. 7

Percentage of particles smaller than 25 microns in the solids whichreport to the underflow stream The figures speak for themselves. Inother tests on a variety of cyclones incorporating the presentinvention, no difiiculty has been experineced in obtaining a thickunderfiow.

Conventional hydro-cyclones are easily adapted for the purposes of theinvention. Thus the cone piece could be inserted in the interior of anyconventional hydrocyclone, thus dividing it into a main hydro-cycloneand a cyclonic chamber. Of course, tangential feed ports should beformed in the cyclonic chamber. Alternatively, the chamber could beadded on to a conventional hydrocyclone. Where a tapering hydro-cyclonehas to be modified, the narrow end is usually cut oil and a continuingcyclonic chamber is added on. The latter may have first a cylindricalsection and then also a tapering section as in a normal cyclone. Theadaption of known cyclones for the purposes of the invention offers nodifficulties.

In FIGURES 2 to 4 further adaptations of known types of hydro-cycloneshave been illustrated diagrammatically. These figures require noelaboration excepting to point out that the main cyclonic chambers havebeen marked 5, the cone pieces 11 and the additional cyclonic chambers13 as was the case in the embodiment of FIGURE 1. Many more variationson the same theme are possible.

We claim:

Apparatus of the hydro-cyclone type for separating fines from coarseparticles contained in a liquid feed, comprising: a main verticallydisposed cyclonic chamber circular in section, at least a portion ofsaid chamber being frustoconical in configuration with the walls con- 5verging toward the lower end of said chamber, the apparent apex of saidfrustoconical portion having an acute included angle in vertical sectionsubstantially less than 90; means including a feed duct communicatingwith said chamber near its upper end for introducing said liquid feedand for imparting cyclonic movement to material Within the chamber tocause said coarse particles to move outwardly to form an underfiowtraveling downwardly in said chamber, a portion of said fines beingentrained in the voids among said coarse particles; 21 second duct 15extending into the chamber at said upper end, the lower open end of saidsecond duct being substantially aligned with the axis of the chamber,the duct serving as a vortex finder to provide an outlet for an overflowcomprising said liquid and the non-entrained fines; a party Wallsubstant'ially frustoconical in configuration with its concave sidefacing said main chamber and with its perimeter contacting the lower endof the frustoconical portion of said main chamber to form the lower endwall of said main chamber, said party wall having a central openingforming an outlet for said undertlow from said main chamber, theapparent apex of said frustoconical party wall having an obtuse includedangle in vertical section substantially greater than 90 to cause anabrupt change in the direction of movement of said underflow so that ittravels inwardly toward the axis of said chamber to materially slow itsdescent prior to passing through said central opening; a secondvertically disposed cyclonic separating chamber on the convex side ofsaid party wall, said second chamber being circular in section with itsaxis coincident with the axis of the main chamber, said party wallforming the upper end wall of the second chamber, said second chamberhaving an opening in its lower end forming an underfiow outlet; andmeans for introducing a wash liquid into the second chamber near itsupper end in the region of said party wall in a tangential directionthat is the same as the direction of cyclonic movement of material inthe main chamber, said wash liquid removing the fines from the coarseparticles and passing back into said main chamber.

References Cited in the file of this patent UNITED STATES PATENTS I2,252,581 Saint-Jacques Aug. 12, 1941 2,312,706 Freeman Mar. 2, 19432,794,832 Rietema June 4, 1957 FOREIGN PATENTS 827,491 Germany Jan. 10,1952

